Method of manufacturing boots,shoes and the like



P 1970 I J. D. CARRIERO 3,526,579

METHOD OF MANUFACTURING BOOTS, SHOES AND THE LIKE Filed Oct. 23, 1967 FIG.2

INVENTOR JOSEPH D. CARRlE RO ATTORNEY United States Patent 3,526,579 METHOD OF MANUFACTURING BOOTS, SHOES AND THE LIKE 1 Joseph D. Carriero, 128 Sandringham Drive, Toronto, Ontario, Canada Filed Oct. 23, 1967, Ser. No. 677,397 Int. Cl. C23]: 7/02 U.S. Cl. 204-9 10 Claims ABSTRACT OF THE DISCLOSURE This invention provides a method of manufacturing master molds for use in the slush casting process for the production of plastic footwear, which method is characterized by a first step of using a true prototype boot as contrasted with the usual starting mock-up. The invention also provides a method of slush casting plastic boots, including the manufacture of a master mold beginning with a true prototype boot.

This invention relates to the manufacture of boots and shoes and is primarily concerned with the manufacture of molds used in the production of plastic footwear by slush casting.

The manufacture of plastic footwear by slush casting is carried out by filling a mold with a liquid plastic resin and pouring out the bulk of the resin following setting of a layer of the resin against the inside surface of the mold. The process is usually repeated several times to build up the desired wall thickness in the piece of footwear.

Heretofore the molds have been prepared by starting with a mock-up of a finished boot and by a series of intermediate steps eventually producing a plurality of production molds. The mock-up has normally been constructed by gluing pieces of leather or other boot material to a wooden form. Thus, the shape of the resultant mold is derived from the shape of the form while the surface finish of the mold is derived from the pieces of boot material attached to the form. However, the molds resulting from this process are not capable of producing final products which are truly natural in appearance. The shape of the final boot is quite artificial as it is not possible to build a wooden form that has the creases and the like of an actual boot. Further, the surface finish of the final product is also likely to be quite artificial as it will often show the junction lines between the various pieces of leather used to cover the form while such natural features as stitching and the like are absent. In the result, plastic footwear made heretofore by the slush casting process have not had truly naturally appearing surface finishes or shapes.

It is, therefore, the chief object of this invention to provide a slush casting method for the production of footwear which will produce boots and shoes having truly naturally appearing shapes and outer surface finishes simulating leather, leatherette or other foot-wear materials.

The above and other objects of the invention are accomplished by the manufacture of a master mold from an actual prototype formed of the material having the surface finish, such as grain, which it is desired to reproduce in the final product and having a true boot shape as contrasted with the known methods of making the master mold from a mock-up having only an artificial shape and surface finish.

The invention will be more thoroughly understood from the following description of several preferred embodiments thereof as read in conjunction with the accompanying drawings.

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In the drawings which illustrate two steps of one preferred embodiment of the invention,

FIG. 1 is a perspective view of a prototype boot as it is being preliminarily prepared for electroplating; and

FIG. 2 is a perspective view, partly broken away, of the prototype boot illustrated in FIG. 1 as it has been prepared and positioned for electroplating.

The prototype boot 10 illustrated in the drawings is an actual boot formed of the particular material that it is desired to imitate in the slush cast plastic final prod uct. In other words, if it is desired to produce a plastic boot having a surface finish similar to leather, the prototype boot will actually be formed of leather. Alternatively, of course, if it is desired that the final product has a surface finish similar to leatherette or plastic, the prototype boot will be formed of these materials. As previously mentioned, the known methods of producing master molds have always started with a mock-up formed of pieces of boot material glued to a wooden form.

In accordance with this invention, the first step in producing a master mold from an actual prototype is to remove from the latter its lining, binding, buckles, zippers, ornaments and the like. Then an extension 12 up to 3 inches in length formed of leather or plastic is cemented to the inside of the top lining of the prototype with the extension being slightly flared outwardly towards its upper end. The prototype is then made rigid in its natural shape and this is preferably accomplished by coating the inside surface of the boot and its extension with a beeswax compound 14 and while the final wax coating is still warm, the foot portion of the prototype is filled with a granular material such as bird cage gravel and the prototype is shaped in the vamp and quarters as required. Excess granular material is poured out following hardening of the wax coating.

The outer surface of the prototype is now prepared for I electroplating. This is done by filling with as little wax or other thermoplastic filling compound as necessary to present a good plating surface all grooves such as between the outsole and the upper, heel and upper, as well as along the edges of the lapped seams and overlays. A preferred method of filling these grooves is with a small electric heating element having a pennib shaped point. In addition to filling the grooves previously mentioned, all pin holes, scratches, cracks, etc. are also filled with wax. To coat the front and back closing seams without blocking out the stitches by the application of excess wax, it is preferred to apply as paste Wax to these areas with all excess being wiped off with a rag.

' Finally, the bottom of the sole is prepared by cementing to it any size symbol or other symbol such as trade names and waxing around their edges with hot wax. The prototype model is then ready for racking which is a trade term referring to preparing the prototype for hanging in its electroplating bath.

The first step in racking the prototype is to fix a wood or the like ring 16 within the top lining of the extension 12 as by passing staples 18 through the extension into the ring. Then a specially shaped metal hanger is fixed to a ring by a short piece of wire 20. This hanger is preferably formed of quarter inch copper rod bent to shape so that it will support the prototype boot from the toe to the top of its shaft. It is insulated along its full length with the exception of a portion at its uppermost end. The insulation can be applied by heating the rod and dipping it in plastisol so that the preheating of the rod cures the plastisol. Alternatively, plastisol may be applied to cold rod material and cured in an oven.

As shown in FIG. 2, the upper end of the hanger which is hook-shaped is engaged over a cathode rod 22 and an electrical connection between the upper end of the hanger and the outside surface of the prototype is effected by wrapping a piece of copper or the like wire 23 tightly about the outside surface of the extension and around ring 16 with the wire being attached to the upper end of the hanger. To guide the wire, tacks 24 are driven partially through the sides of the boot.

The prototype boot is now given a final cleaning with naphtha gas in the case of leather or tolual or alcohol in the case of a plastic prototype. When working with a leather prototype, the naphtha gas is allowed to thoroughly dry and a protective coating, such as an acrylic lacquer, is sprayed over the entire surface of the prototype and allowed to dry.

The next step is to render the outer surface of the prototype electrically conductive which is done by coating the surface of the prototype with a conductive compound. The two compounds that might be used are graphite and silver nitrate, with the latter being preferable. Silver nitrate coating solutions are available commercially and are easily applied by spraying with an air brush. In spraying, it is important to build up a sufiicient thickness of the silver nitrate to adequately metallize the suface to render it conductive without blocking out fine details such as stitching, leather grain, etc. To accomplish this object, it is preferable to apply the silver nitrate in two coats with the first coat being a very light one which will detail surface imperfections which can be filled in with hot wax before application of the second coat.

An alternative method of silvering is to use other commercial equipment which employs a double nozzle spray gun which emits a different solution from each nozzle which, on converging on the boot, forms a silver coating by chemical action. This particular process, however, is more time-consuming than the previously described silvering method.

With the completion of the silvering to render the outer surface of the prototype electrically conductive, the prototype is now ready for electroplating. However, before electroplating is commenced, the model is weighed so that the desired thickness of the electroplated layer can be produced by periodically weighing the prototype as to measure the amount of material that has been deposited. Electroplating is started by submerging the racked prototype in a sulphamate, kept at a preferred temperature of 70 to 130 F., and for the first half hour the plating voltage is set at 1 volt and increased at the end of this period to 1 /2 volts for 1 hour. At this time, the power is reduced to 1 volt and the prototype removed from the bath for inspection to see if the electroplating has begun to take satisfactorily. If not, the prototype may be salvaged by cleaning and stripping off the thin shell of nickel that has been deposited. After electroplating has commenced in a satisfactory manner, the boot is returned to the tank and a current density of 5 amps per square foot of boot area is set up. After minutes at this setting, the current is increased to 12 amps per square foot and retained at this level for approximately 24 hours. At the end of this period the power is reduced to 1 volt, the boot removed and rinsed in clean water for the removal of any scum or salts and then very quickly immersed in a tank of copper sulphate solution. A preferred solution is copper sulphate 30 oz./gal., sulphuric acid 7.5 cz./ gal. and water, kept at a temperature of 70 to 90 F. In the copper tank the current density is set at amps per square foot and after about 14 hours. weight checks are started and copper plating is continued until the desired thickness of electroplated material has been built up as determined by the weight checks.

Upon completion of electroplating, the wire 23 is cut off and the wooden insert 16 removed, then the electroplated prototype is heated in boiling water in order to soften the wax filling or the wax is softened in an oven. With the wax still hot, the boot shaft is freed from the electroplated mold by hand as far down as can be reached and the prototype is then stripped from the mold by a large pair of pliers or the like.

As a final step, the mold is now cleaned to remove any silver spray which has been transferred from the model. This is done by first washing the inside of the mold with trichlorethylene which removes a certain amount of the silver coating. The remainder of the silver is removed by slush casting three or four plastic skins, each one of which takes a considerable amount of the remaining silver with it. Finally, the mold is acid polished with a solution of 16 parts sulphuric acid to 4 parts nitric acid to 1 part water. This acid solution is poured into the mold and allowed to stand for twenty-five to thirty minutes and then drained out. The acid is removed by water washing. At this point, the master mold has been completed.

From each master mold there is next produced a plurality of production molds, with the number of production molds being formed depending upon the number of boots or shoes that it is desired to produce.

The production molds are essentially made by slush casting a number of production skins and then electroplating the production molds on these skins in the same manner in which the master mold was produced from the original prototype model. The production skins are slush cast using a combination of plastisol and thermasol which gives a rigid model which will stand up without requiring a wax treatment. These production skins are then prepared for plating in the same manner in which the prototype is prepared. However, before silvering and electroplating the production skins, the latter are placed in very hot water for 15 minutes or so following stripping from the master mold so they wil conform back to their proper size and shape should they have stretched when being stripped from the master mold. Prior to silvering, the plastic production skin is given an overall washing with methyl ethyl ketone which brightens the plastic and shows up any defects. At this point, minor pits or air holes can be repaired by filling them in with a small amount of liquid plastic and heating the latter with a hot air gun. Racking, silvering and electroplating of the production skins to produce the production molds is carried out in the same manner as previously described with respect to the preparation of the master mold. The one difference is that following electroplating of the production molds and stripping the production skins therefrom and cleaning, etc., the production molds are cut off at the top so that the final product will have the desired height. In the normal course, the height of the shaft of the production mold is 1% inch above the desired height of the final product.

While the foregoing refers to electroplating with nickel and then copper, it should be understood that the master and production molds may be formed of either one of these metals alone or of zinc or tin, or combinations thereof.

What I claim as my invention is:

1. A method of manufacturing a master mold for use in the production of plastic footwear by slush casting, said method comprising the steps of taking a premade prototype footwear piece having the shape and surface finish it is desired to reproduce in a plastic footwear piece, extending the shaft length of the prototype by fixing a shaft extension to the top thereof, making rigid the prototype footwear piece by coating its inside surface and the inside surface of the extension with a low melting point thermoplastic material, preparing the outside surface of said prototype for electroplating by filling in the imperfections therein and coating all grooves, lap seam edges and overlays with a filling compound compatible with the material of which said prototype footwear piece is made rendering the outside surface of the prototype electrically sensitive by applying a coating of an electrically conductive material, racking the phototype preparatory to plating the outside surface thereof by suspending the prototype boot from a cathode bar by a hook and making an electrical connection between said cathode bar and the outside surface of said prototype, immersing the prototype in a bath of an electrolytic solution of a metal selected from the group consisting of nickel, copper, zinc or tin and feeding electrical current to the outside surface of said prototype through said cathode bar as to electroplate a layer of metal onto the outside surface of said prototype, removing said prototype from said bath and softening and removing the thermoplastic material from the inside surface of said prototype and its shaft extension, and stripping the prototype from the master mold consisting of said electroplated metal layer.

2. A method of manufacturing a master mold for use in the production of plastic footwear by slush casting, said method comprising the steps of taking a premade prototype boot having the shape and surface finish it is desired to reproduce in the plastic boots, extending the shaft length of the prototype by fixing a shaft extension to the top thereof, making rigid the prototype boot by coating its inside surface and the inside surface of said extension with a wax compound, preparing the outside surface of said prototype boot for electroplating by filling in imperfections therein and coating all grooves, lap seam edges and overlays, with wax, rendering the outside surface of the prototype boot electrically sensitive by applying a coating of an electrically conductive material, racking the prototype boot preparatory to plating the outside surface thereof by suspending the prototype boot from a cathode bar by a hook and making an electrical connection between said cathode bar and the outside surface of said prototype boot, immersing the prototype boot in a bath of a nickel salt solution and applying electrical current to said racked and immersed prototype boot so as to electroplate the outside surface thereof with a layer of nickel of predetermined thickness, removing the prototype boot from said nickel salt solution bath and immersing same in a copper salt solution bath and electroplating a copper layer of predetermined thickness to said nickel layer, removing said prototype boot from said copper salt solution bath and softening and removing the wax from the inside surface of said prototype boot and its shaft extension and stripping the latter from the nickel copper female master mold and cleaning the inside surface of said master mold.

3. A manufacturing method as claimed in claim 2 in which said electrically conductive material used to sensitize the outside surface of said prototype boot is selected from the group consisting of graphite and silver nitrate.

4. A manufacturing method as claimed in claim 3 in which said electrically conductive material used to sensitize the outside surface of said prototype boot is silver nitrate.

5. A manufacturing method as claimed in claim 4 in which said silver nitrate is applied in the form of a one to one solution of silver nitrate in butyl acetate by spraying in a three-step procedure consistng of the application of a first thin silver nitrate layer, filling in imperfections in said first silver nitrate layer with hot wax and the application of a second layer of silver nitrate.

6. A manufacturing method as claimed in claim 5 in which said nickel salt solution is a solution of nickel sulphamate in water.

7. A manufacturing method as claimed in claim 6 in which said copper salt solution is a solution of copper sulphate in water.

8. A manufacturing method as claimed in claim 7 in which said electroplating of the nickel layer is carried out for approximately twenty-four hours at a voltage of 1 volt for 30 minutes, 1 /2 volts for the next minutes, and at a subsequent current density of 5 amps per square foot of boot surface area for 15 minutes and, finally, at 12 amps per square foot of boot surface area for the remainder of the twenty-four hour period.

9. A manufacturing method as claimed in claim 8 in which said copper layer electroplating is carried out for approximately twenty-four hours at a current density of 20 amps per square foot of boot surface area.

10. A manufacturing method as claimed in claim 9 in which said wax in the prototype boot is softened following electroplating by heating the prototype boot in boiling water.

References Cited UNITED STATES PATENTS 2,912,368 11/1959 Bingham 204-9 2,949,410 8/1960 Bingham 204-9 3,068,156 12/ 1962 Efron 204-9 3,158,558 11/1964 Bingham 204-9 I. H. MACK, Primary Examiner T. TUFARIELLO, Assistant Examiner 

